Active air heater

ABSTRACT

An active air heater is constructed to produce heat and to transfer heat to an air flow for heating a building. The active air heater comprises spaced apart fins; adjacent elements between the fins; and an electrical source directing an electrical current through the fins and the adjacent elements for heating the fins and the adjacent elements and the air flowing through the air flow passageways formed by the adjacent elements. The adjacent elements are porous, semi-conductor material having a roughness in its surfaces for enhancing the convective heat transfer between the material and the air flow. The active air heater may be rectangular or cylindrical. The porous, semi-conductor material includes carbon foams, ceramic foams, high temperature polymer foams, and low conductance alloy foams and the aforementioned materials in nano-material format.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Ser. No. 61/280,803, filed Nov. 9, 2009, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an active air heater that uses electric resistance heating and effective convection heat transfer to heat air without the involvement of any working fluids or open flames. More specifically, the present invention relates to an active air heater that heats a heat exchanger and transfers the heat from the heat exchanger hardware to the air.

2. Description of Related Art

An active air heater is different from the traditional resistance heaters, the traditional boiler/air handler heating systems, and infrared heaters. The traditional resistance heating generally requires that high resistance heating elements be heated. A relatively small space can be heated using resistance heating since the surface area of the heating elements is generally small. The traditional boiler and air handler heating systems use hot water or steam as a work fluid to transfer the heat to the air flow in the air handler. Infrared heaters transfer thermal energy through electromagnetic waves.

It is well known that a boiler/air handler heating system works as follows: The boiler in terms of conditioning the air generates steam or hot water as a work fluid mixture and sends this work fluid through insulated pipelines in a building and to the copper coils of an air handler. An air handler, also referred to as an air handling unit (AHU), in general, is a device used to condition and circulate the air as part of a heating, ventilating, and air-conditioning (HVAC) system. An air handler may be a large metal box containing a blower or fan, heating and/or cooling elements, filters, a humidifier, mixing chambers, sound attenuators, and dampers or vibration isolators. Air handlers generally connect to the ductwork, which, in turn, distributes the conditioned air throughout the interior of the building and returns air to the air handling unit.

In the winter months, the air handler heats the air by forcing the air flow between the copper coils containing the steam or hot water from the boiler. This heated air is mixed with additional air, including outside air, in the air handler and is distributed by the air handler through the hot air ducts and into the interior of the building, and the cool air is brought back into the air handler through the cool air ducts.

The boilers used in large commercial buildings are capital equipment and expense, and require yearly maintenance including leakage testing of the coils and repairs. Boilers are the most commonly used equipment that converts fuel or electricity into the thermal energy carried by the work fluid (hot water or stream). Boiler efficiency has been improved significantly. However, certain energy losses can not be avoided such as the thermal energy loss occurring during the water heating process and a pressure energy loss occurring when transporting the heated water from the boiler to the heating coils inside an air handler. The pressure energy loss is caused in transporting the hot water or steam from the boiler room which generally is located in the basement of the building and up to the air handler which generally is located at the top of the building. The pipeline installation for transporting the hot water or steam from the basement up to the top of the building adds to the building construction costs.

There is a need to provide a heating device that lessens or eliminates the thermal and pressure energy losses associated with present day heating systems.

There is a further need to provide a heating device that is lightweight and has a simple construction, a high efficiency energy transfer, low construction costs and little or no maintenance compared to present day heating systems.

SUMMARY OF THE INVENTION

The present invention has met these needs. The present invention provides an active air heater that is easily integrated in air moving equipment such as an air handler or an air blower. The active air heater uses electric resistance heating and effective convection heat transfer to heat air without the involvement of any working fluids or open flames. More specifically, the active air heater of the present invention heats a heat exchanger and transfers the heat from the heat exchanger hardware to the air. The heated air flows into a designated space, such as a building to heat the building. The active air heater is a solid air heat exchanger that actively heats the air by the temperature gradient between the heat exchanger itself and the air. Different from conventional resistance heating space air heaters, the main heat transfer of the active air heater of the invention is not radiation heat transfer, but is convection heat transfer. The active air heater has a large surface area and a high solid-to-air heat transfer rate. The active air heater of the invention transfers thermal energy from a solid directly to the air instead of from one fluid to another through a solid separator of an air heat exchanger.

The active air heater of the invention can easily be integrated into traditional duct systems to replace the coils in the boiler/air handler system; however the installation and maintenance costs are greatly reduced compared to present day boiler/air handler systems. In addition, the active air heater has all the flexibility of any resistance heater for effective distribution of thermal energy inside the space of interest.

The active air heater comprises at least two spaced apart fins comprised of electrical conductive material with reasonable but variable resistance (e.g. from 5 to about 1 million ohms); a plurality of stacked elements located between the fins and in direct contact with the fins, the plurality of stacked elements forming one or more air flow passageways; and a source of electricity which may be either an alternate current (AC) source or a direct current (DC) source for directing an electrical current through the spaced apart fins and through the plurality of stacked elements for heating the stacked elements and the air flowing through the air flow passageways.

The elements comprise semi-conductor material with a large surface area. The semi-conductor material includes porous, semi-conductor material and porous materials. Suitable porous, semi-conductor material includes carbon foams, ceramic foams, high temperature polymer foams, and low conductance alloy foams. Suitable porous materials include conventional porous materials and conventional porous materials with partial nano-material components or nano-materials.

The stacked elements are constructed to function as a combination heating element and heat exchanger for the air flowing through one or more air flow passages, and at least one of the electrically heated elements comprises a connector plate or other forms of connection for attachment to the air handler. The heater dimensions can be from a few cubic inches up to any size required by the end application.

The active air heater of the invention has either a rectangular or a cylindrical configuration wherein the electrically heated fins can be rectangular elements, in straight or curved format, and/or pins with various cross-sectional shapes. If the active air heater is cylindrical, the air heater has a lower section having one or more air flow passageways for transporting air into the active air heater and heating the air, and an upper section having one or more air flow passageways for receiving the heated air from the lower section and heating the heated air and directing the heated air out of the active air heater.

The elements of the active air heater are heated by running an AC or DC current through the elements. The air is heated when flowing through the stacked elements. The active air heater may in some embodiments be at the same location as the air handler and may be physically connected to and/or in communication with the air handler through the building ductwork. Additionally, when heating an industrial manufacturing space, a system including the air active heater of the invention with an air moving device, such as a fan, may be located and relocated anywhere in the building to accommodate the needs of the building occupants.

These and other aspects of the present invention will be more apparent from the following description when read in light of the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an active air heater of an embodiment of the present invention.

FIG. 2 is a schematic of an active air heater of a further embodiment of the present invention.

FIG. 2A is a section view of the active air heater of FIG. 2.

DESCRIPTION OF THE INVENTION

The present invention provides an active air heater. The term “active air heater” refers to an air heater that performs at least two functions simultaneously, which are to: 1) produce heat; and 2) via the heating elements, effectively and directly transfer the heat to an air flow passing through the heater without the involvement of other fluids, such as water. The active air heater of the invention may comprise one or more elements that are in effect a combined heating element and air heat exchanger. A heating element normally has a small surface area per unit bulk volume that only provides a heat source, and a heat exchanger mainly transfers heat from one work fluid to another but does not produce heat. The active air heater of the invention is structured to produce heat from electricity and to transfer the heat directly to the air flow effectively due to the large surface area of the heating element material such as that, for example, disclosed in the following paragraph.

FIG. 1 illustrates an embodiment of an active air heater 10. As shown, active air heater 10 comprises spaced apart electrically heated adjacent plates or elements 12, 14 and 16; and an electrical supply source (not shown), which may be DC or AC current, for electrically heating elements 12, 14 and 16. Elements 12, 14 and 16 are bonded together through suitable means to form a bonding seam there between as indicated at reference numeral 13 for elements 14 and 16, and to form a series of air flow passageways 18, 20 and 22. As shown in FIG. 1, elements 12, 14 and 16 are located between two spaced apart fins 15 and 17 and electric current is directed into fin 15 and through elements 12, 14 and 16 as shown by arrow A and out of fin 17 as shown by arrow B. In some embodiments, fins 15 and 17 are comprised of an electrical conductive material with reasonable but variable resistance, such as for example, 5 to 1 million ohms. In some embodiments, elements 12, 14 and 16 may be comprised of a porous, semiconductor conductive material. Suitable electrically semi-conductor materials (generally referred to herein after as “semi-conductor material”) include: carbon foams; ceramic foams; polymer foams or alloy foams; materials made with carbon, ceramic, polymer or an alloy in a porous or partially porous state; solid semi-conductor materials with rough surfaces; and the aforementioned traditional materials in nano-material forms.

Electrical current flows into and heats elements 12, 14 and 16 and the generated heat is transferred into the air flow pathways 18, 20 and 22. Air flows are generally in the same direction, which with regard to FIG. 1 is perpendicular to the plane of the paper. Air flows can be in different directions if two or more outlets are desired. Or, as illustrated in the cylindrical configuration of air heater 30 of FIG. 2, the air flows can be distributed 360 degrees out into the space to be heated.

The semi-conductor material of elements 12, 14 and 16, in some embodiments, may comprise surface areas of a certain degree of roughness, particularly on the external surfaces for enhancing the convective heat transfer at the surface.

FIGS. 2 and 2A illustrate a further embodiment for an active air heater 30 of the present invention. Active air heater 30 is in a substantially cylindrical configuration and comprises one or more adjacent circular sections 32 and 34. Active air heater 30 is generally designed to distribute several flows of heated air in a 360 degree configuration out into a large floor area, generally, of commercial and/or industrial buildings.

As shown in FIG. 2A, upper section 32 has a central passageway 38 and lower section 34 has a central passageway 36 in alignment with central passageway 38 along a center line CL. Upper section 32 further includes several air flow passageways 40, 42 and 44 for directing heated air out of active air heater 30, and lower section 34 further includes several air flow passageways 46 and 48 for directing cool air into the lower section 34.

Referring particularly to FIG. 2, upper section 32 and lower section 34 are electrically heated by directing an electrical current into upper section 32 as indicated by arrow C and through lower section 34 as indicated by arrow D. Even though not shown in FIG. 2, a fin similar to that shown for elements 12, 14 and 16 of FIG. 1 may be provided at opposite ends of the active air heater 30 adjacent to upper section 32 and lower section 34, respectively.

In some embodiments, upper section 32 and lower section 34 are comprised of semi-conductor material. The semi-conductor material is preferably, porous semi-conductor material. Suitable porous semi-conductor material includes lower grade carbon foams, ceramic foams, high temperature polymer foams, and low conductance alloy foams. The heat generated in upper section 32 by the electrical current is transferred from the areas forming passageways 40, 42 and 44 and into the air flowing through passageways 40, 42 and 44. Similarly, the heat generated in lower section 34 by the electrical current is transferred from the areas forming passageways 46 and 48 in lower section 34 and into the air flowing through passageways 46 and 48 to heat the incoming air as shown by the arrows in the lower section 34 of FIGS. 2 and 2A. This heated air from the air flowing through passageways 46 and 48 flows into central passageway 36 of lower section 34 and central passageway 38 of upper section 32 and into passageways 40, 42 and 44.

A fan (not shown in FIGS. 2 and 2A) may be attached to the top portion of the air heater 30 to create a pressure gradient to force air flow upward and then outward along the radius of air heater 30. Natural convection will further assist the upward flow of the air as the heated air tends to rise up inside air heater 30, hence, enhancing the internal air flow.

Similar to the embodiment of FIG. 1, the active air heater 30 of FIGS. 2 and 2A may include an electric power supply source as indicated at reference numeral 50. The surface temperature of elements 12, 14 and 16 of FIG. 1 and the surface temperature of upper and lower sections 32 and 34 of FIGS. 2 and 2A may be about 125.7 degrees F. This surface temperature range may be generated by using a 1.65 volt DC battery charger applied to elements 12, 14 and 16 and upper and lower sections 32 and 34. Higher temperatures may be achieved by using higher current densities. However, while higher temperatures enhance heat transfer, the design of the active air heater of the invention may have to tackle issues caused by the higher thermal stresses among dissimilar materials when the temperature is too high. The elements 12, 14 and 16 of the active air heater 10 of FIG. 1 and sections 32 and 34 of the active air heater 30 FIGS. 2 and 2A will generally be designed to not exceed 350 degrees F. A connector plate may be used to attach the active air heater to an air handler.

For resistance heating, the electrical energy input into the active air heater of the invention will about equal the thermal energy output of the active air heater of the invention. Based on fluid mechanics theory and validated by the inventor that among the various types of semi-conductor materials commercially available, that the porous, semi-conductor materials may in some embodiments be desirable since the heating rate for porous, semi-conductor materials may be generally higher compared to solid materials that have smooth, uniform surfaces.

The active air heaters 10 and 30 of the invention may have certain advantages over the traditional heating systems, such as space heaters and boiler/air handler systems. The advantages may become more obvious in the environment of more renewable energy. Electricity is the format of the energy storage and energy output from many renewable energy sources.

Some advantages of the active air heater of the present invention include:

-   -   Simplicity and low maintenance. The active air heater of the         invention can be operated with electricity only. No steam or         water and no steam pipelines and coils are required.     -   Low energy losses. The active air heater of the invention can be         integrated into air handlers at the same location. Very little         energy is lost. In contrast, the steam pipelines could lose         thermal energy and pressure head along the long transportation         route from the boiler to the air handler according to current         day boiler systems.     -   Wide range of energy sources. The active air heater of the         invention can be operated by an AC or DC power source with         voltages as low as 2-3 volts. This advantage enables the active         air heater to be operated by a wide range of energy sources,         such as for example solar units, batteries, natural gas, etc.     -   Low costs. The active air heater of the invention has a low cost         due to its simplicity in design that innovatively combines the         heat transfer principles with the material characteristics. The         fact that the material of the heater elements is produced from         inexpensive and abundant precursor material predicts another         potential for lower material cost.     -   Active air heater. The active air heater of the invention is         active in that it combines the functionality of a heating         element and a heat exchanger. It is heated by electricity with         about a 100% conversion rate and the air passing through the         heater 10 and 30 is heated by the heating elements thereof.     -   Flexibility. The active air heater of the invention can be         removed, replaced, and/or reused. It can vary in size and         control settings depending on the needs of the zones covered by         an air handler. Additionally, the active air heater of the         invention can be installed almost anywhere in a building. This         feature is particularly useful for historical buildings where         adding an entire steam pipeline network could be costly and         unsightly, and at times, impossible.     -   Other applications. The active air heater of the invention can         be used for medical applications, rehabilitations, vehicles,         aircrafts and instruments where a low voltage heat source is         needed.     -   Scaling up. Electric heating is already used in buildings and         other industries. Scaling up the capacity of the active air         heater of the present invention for a very large commercial         complex is a low risk.     -   Diverse applications. The active air heater of the invention may         be used in residential buildings, commercial buildings, and         industrial buildings. FIG. 2 illustrates an active air heater 30         having heated air being distributed circumferentially there from         for a 360 degree heating area. This configuration may be         suitable in industrial buildings where the heating of a large         work area at about six feet from the ground and may be the most         efficient configuration for the active air heater.

As disclosed herein above, the active air heater of the invention may be attached to an air handler and may be controlled by the building control system for the zone or zones controlled by the air handler. The active air heater of the invention is anticipated to have high efficiency and is easily scalable to large buildings especially for large commercial complexes. The benefits may include an energy savings of about 15% to about 40%, in addition to significantly reducing the initial capital expenditure in building costs, with less utility and maintenance costs and locally controllable heating for the building occupants. The active air heater of the present invention may be located in close proximity to the air handler; and is desired to accommodate any type of building.

The active air heater of the invention can have dimensions that can be from a few cubic inches up to any size required by the end application.

From the above description, it will be appreciated that an active air heater of the invention could be installed at the same location as the coils inside an air handler. The boiler and pipelines can be replaced with electric wires from the breaker box to the air heater. For a non-central heating system, or an auxiliary heating system, the active air heater of the invention can be located at any location in general This flexibility in locating the active air heater of the invention may be an important feature for effective thermal energy distribution inside a building. Buildings do not need to be heated uniformly, especially very large commercial buildings or manufacturing plants or large public buildings, such as, for example, a big church or an opera house. Normally, only six feet above the floor level needs to be heated for the building occupants. Traditional central heating systems oftentimes have tough design decisions regarding effective heating. With the active air heater of the invention, effective and efficient heating can be realized without sacrificing other design requirements.

The active air heater of the invention has the added benefits of being light weight and having a simple construction, high heat transfer efficiency, low construction costs, flexible locations, and little or no maintenance. The active air heater of the present invention does not use very high resistance heating elements but provides a very large surface area for effective convective heat transfer. The active air heater of the invention does not require any work fluid and does not rely on electromagnetic wave radiation.

While the present invention has been described in connection with the embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiments for performing the same function of the present invention without deviating there from. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims. 

1. An active air heater comprising: spaced-apart fins comprised of electrically conductive material; a plurality of adjacent elements between the spaced-apart fins and forming one or more air flow passageways; and a source of electricity for directing an electrical current through the spaced apart fins and through the plurality of adjacent elements for heating the adjacent elements and the air flowing through the air flow passageways.
 2. The active air heater of claim 1 wherein the plurality of adjacent elements comprises semi-conductor material.
 3. The active air heater of claim 2 wherein the semi-conductor material comprises porous semi-conductor material.
 4. The active air heater of claim 3 wherein the porous semi-conductor material comprises carbon foams, ceramic foams, polymer foams, and low conductance alloy foams.
 5. The active air heater of claim 1 wherein the plurality of adjacent elements are constructed to function as a combination heating element and as a heat exchanger for the air flowing through one or more air flow passageways.
 6. The active air heater of claim 1 further comprising a connector plate for attachment of the active air heater to an air handler.
 7. The active air heater of claim 1 wherein the active air heater comprises a substantially rectangular configuration wherein the fins are substantially rectangular.
 8. The active air heater of claim 1 wherein the active air heater comprises a substantially cylindrical configuration and wherein the electrically heated elements are substantially cylindrical.
 9. The active air heater of claim 8 wherein the active air heater comprises a substantially cylindrical configuration and further comprises, a lower section comprising a plurality of air flow passageways for transporting air into the active air heater and heating the air; and an upper section comprising a plurality of air flow passageways for receiving the heated air from the lower section and further heating the heated air and directing the heated air out of the active air heater.
 10. The active air heater of claim 1 wherein the source of electricity includes AC and DC current sources. 